The proposal describes plans to extend our understanding of the effects of lithium on stimulus-response-coupling via phosphinositide metablism in the central nervous system with emphasis on those effects in vivo. A major thrust of the work is the analysis of this pathway through measurements of the effects that experimental procedures have on the products of that metabolism, the inositol phosphates. The plan is divided into five related proposals. 1) The development of chemically-specific non-radiometric methods, suitable for in vivo research, for the analysis of myo-inositol 1:2-cyclic phosphate and the inositol polyphosphates, methods that are presently unavailable. 2) The identification of the origin of the myo-inositol-1-P that accumulates in rat brain following lithium treatment and treatment with lithium and centrally-acting agonists, i.e., is it from phosphatidylinositol or from polyphosphoinositide metabolism? We have evidence suggesting the former, which raises the question as to what function this metabolism serves if not the second-messenger role to the polyphosphoinositides. 3) using the methods we develop, measure tht inositol phasphate products of polyphosphoinositide metabolism in vivo in experiments with lithium and with lithium and other agents. These experiments are designed to establish the dynamics of that metabolism in vivo and to provide a basis, in substrate amount, for comparison with in vitro work of our own as well as the work of others. The experiments will also reveal how lithium affects other steps in this pathway in vovo, important because there is in vitro evidence from other laboratories that there are such effects but the current state of the methods in this field are the limiting elemet for further study. 4) Continue our studies to test the theory that lithium, by inhibiting myo-inositol-1-phosphatase, limits the response of phosphoinositide-linked receptors by causing inositol levels to decline to substrate-limiting levels in highly-stimulated polyphosphate cells. No direct evidence yet supports that theory. 5) Purify the inositol phosphatases from brain in order to determine the kinetics of the effects of lithium on these enzymes and to increase our understanding of this highly metabolically-active pathway.